first off, how many DE's in any system have that many sacks their rookie season? even jj watt didn't.
second of all, the chargers didn't bring him in just to sack the QB, he will have to be an effective run stopper and be disruptive as well.
i will say this, if by year 3 he isn't dominating and going to the pro bowl then he will be a bust in my mind. heck if he isn't going to the PB in year two or at least having a PB caliber season i will have serious concerns.